During processing, semiconductor wafers are subjected to numerous process steps in various machines and at various locations. The wafers must be transported from workstation to workstation and from facility to facility. Numerous types of shipping devices have been previously known for handling, storing, and shipping wafers. Such devices hold the wafers in axially aligned arrays with, for example, twenty-five wafer arrays. Where the wafers are shipped from facility to facility and where the containers containing the wafers may be subjected to significant shock, the containers are configured to hold the wafers vertically. A vertical wafer is less prone to damage from shock or vibration than a wafer horizontally suspended by its edges.
A principal component of the shipping containers is a means for cushioning the wafer during transport to protect against physical damage from shock and vibration. Such shipping containers and cushioning means have been previously known as disclosed, for example, in U.S. Pat. Nos. 4,043,451; 4,248,346; 4,555,024; 5,253,755; 5,273,159 and 5,586,658. These types of containers typically included vertical wafer-receiving channels which have been provided with cushions at the upper and lower ends. These shipping devices are designed to transport wafers or disks in a vertical orientation from place to place, whereas conventional processing workstations require removing horizontally the wafers for processing.
With the vertically-oriented carrier, wafer-receiving channels are generally designed to hold wafers firmly with a minimum of horizontal movement. Also such carriers generally allow the wafers to bear against the vertical surfaces of the wafer channels. The vertical slots of such carriers are typically smooth, that is featureless to allow the wafers to be slid in and out of the slots with minimal abrading and scraping. Whereas with the horizontally-oriented process carrier, wafer-receiving channels are relatively larger to enable wafers to be lifted off of seating positions on horizontal wafer shelves and robotically removed from the slot without contact of the carrier by the wafer. Moreover, horizontal carriers now in use for transporting wafers within fabrication facilities, particularly for larger wafers, i.e. 300 mm, are now being designed for minimal contact with wafers. See U.S. Pat. No. 5,788,082 to Nyseth and assigned to the owner of the invention of the instant application. A pair of shelves will contact the bottom side of the wafer at four regions of contact. Each region will be by a protrusion extending from the shelf and will create a point or an abbreviated line contact with the shelf. Such protrusions are not seen in the conventional vertical wafer shippers and such conventional vertical shippers do not provide for this minimal contact. Thus, conventional vertically-oriented carriers are not ideally suited for use as horizontally-oriented carriers, for use as transport modules in fabrication facilities intermediate process steps.
The evolution of wafer processing to larger wafers has exacerbated a phenomena known as "flutter." Flutter is the vibration or bouncing of the wafer on the one restrained side of the wafer, that is, the wafer shelves; or in conventional vertical carriers along the one side of the channel that the wafer is resting against. Such vibration or bouncing is highly undesirable in that it can generate or launch particles in the carrier and damage the wafer. Flutter occurs when the wafer container is subjected to shock. Flutter can occur even where the two opposite ends (front edge and back edge) of the wafer are restrained and the intermediate portion (left edge and right edge) is restrained on only one of the top and bottom surface of the wafer. The flutter phenomena is particularly pronounced in 300 mm wafers now being used in fabrication facilities.
Horizontally-oriented wafer carriers with cushions are known. See U.S. Pat. No. 5,915,562 to Nyseth and Krampotich and assigned to the owner of the instant invention. This patent discloses an active cushion that moves inward and engages the front edges of the wafer after the door is secured in place. Passive cushions mounted to the door on front opening carriers are also known. Such cushioned (passive and active) horizontal carriers still have the wafers restrained intermediate the front and back end on only one surface. Thus, the wafer are subject to flutter. Where such an arrangement is rotated 90 degrees to provide a vertically oriented shipper, the flutter problem can be significant.
A carrier is needed that can function effectively as a vertical shipper that still has the advantages of minimal contact when the wafers are oriented horizontally.